Known Islamists with links to an Islamic State (IS, formerly ISIS/ISIL) executioner fled the UK despite being on bail or banned from traveling, a counter-extremism group claims.

An investigation by the anti-racist group Hope Not Hate indicates up to six jihadists may have been allowed to leave the country, despite them being known to authorities and having had security conditions imposed upon them.

The individuals are believed to have had links with the same UK-based extremist group as Siddhartha Dhar, who is thought to be the ‘new Jihadi John’ British executioner who appeared in a recent IS video.

The men were Junaid Hussain and Abu Rahim Aziz, both later killed in drone strikes in Syria, and NHS surgeon Mirza Tariq Ali, who was killed in a drone strike in Pakistan. Muslim converts Simon Keeler and Trevor Brooks also fled and were later arrested in Hungary.

They all belonged to the proscribed Islamist group Al Muhajiroun.

Dhar, a British-Indian and former bouncy castle salesman from London, is thought to be the masked man who appeared in an execution video in early January, in which he brands Prime Minister David Cameron an “imbecile.”

The revelations will pile pressure on authorities, as Dhar also escaped the UK to join the extremist group while on police bail.

Hope Not Hate coordinator Nick Lowles told the Independent: “We have a situation where at least four individuals who were on active bail and must have been known to the authorities as a flight risk have managed to leave Britain.

“Given all six were linked to banned organizations like Al Muhajiroun, there must be very serious concerns about the apparent ease with which individuals who wish Britain harm are leaving the country,” Lowles said.